ON THE FORMATION OF THE MIXED PYRROLE CATALYZED BY PORPHOBILINOGEN SYNTHASE FROM RHODOBACTER SPHEROIDES

The enzyme porphobilinogen synthase (PEGS) catalyses the formation of porphobilinogen (PEG) from two molecules of 5-aminolevulinic acid (ALA ). It has been claimed that the PEGS from Rhodobacter spheroides is ab le to form a mixed pyrrole, from one molecule of 5-aminolevulinic acid and one molecule of levulinic acid. The chemical synthesis of this mi xed pyrrole allowed to show, that the compound formed from 5-aminolevu linic acid and levulinic acid with PEGS from R. spheroides has not the proposed structure. The putative enzyme catalysed formation of the mi xed pyrrole had been used as an argument for the postulated mechanism of PEGS. In view of our results this line of arguments has to bee re-e valuated.